The present invention relates to a novel method and apparatus for measuring the pH in diapers and other such absorbent articles, and more particularly to a method and apparatus for signaling incipient pathogenic and pathological conditions in the environment of the article.
With the increase of mothers employed away from home, and the increase in adult diaper-wearers, there is strong demand for diapers and other disposable garments that can be worn for longer periods. To meet this demand, superabsorbent and dry-feel materials have been developed. Most diaper products contain materials that can absorb many times their weight in urine. They are normally worn for more than four hours and frequently for eight hours or longer. Superabsorbent diapers that feature leakage barriers have also been developed, as well as new ammonia odor control technologies.
Prior to these new technologies, it was commonly accepted that the human olfactory system was the ideal monitor for sensing the onset of toxic ammonia concentrations. But the new diaper technologies have caused such major changes in the pH levels and in the volumes, concentrations, and migration of ammonia gas in diapers, that olfactory sensing is no longer reliable. In addition, since new diaper technologies channel urine away from the interior surface, leaving a dry feel, the sense of touch can no longer inform the caregiver that the diaper may contain a substantial amount of urine.
Onset toxicity of anhydrous ammonia as a caustic agent occurs at concentrations of 20 to 35 ppm. See NIOSH Criteria for Recommended Standard Exposure to Ammonia #74-136; Proctor et al., Chemical Hazards of the Workplace (2ed. 1988). The human odor threshold for ammonia gas ranges from 5 to 50 ppm, although regular exposure to low levels builds olfactory tolerance for higher levels. In the new diapers, ammonia gas concentrations can quickly reach 50 ppm, but the characteristic ammonia odor is, to some degree, contained within the diaper barriers and/or masked by new technologies designed specifically for that purpose. Thus, there is now a need for other methods to warn caregivers of ammonia build-up.
Within the diapered-area temperature and pH are higher than normal, friction is greater and microbes multiply faster than in non-diapered areas. The skin is wetter than normal, non-diapered skin, and wet skin is more vulnerable to damage than dry skin. The combination of these factors causes or contributes to diaper area pathologies.
Diaper-area temperature, microbiological load, and pH are greater in disposables than in cloth diapers. The higher pH in disposables triggers diaper dermatitis, the most prevalent of diaper area diseases. This disease is caused by the actions of proteolytic enzymes, which metabolize the skin and subcutaneous tissue.
Ammonia dermatitis, another diaper area disease, normally occurs only after healthy skin has been continuously exposed to ammonia at greater than 10,000 ppm for more than 15 minutes. See Procter et al., Chemical Hazards of the Workplace (2nd ed. 1988). In a diapered area where the epidermis has already been compromised, ammonia exacerbates the pre-existing condition.
Urine entering a diaper is sterile and has a pH of about 6.2. Ammonia gas escapes the urine. At this point, the entire diaper-area pH begins to rise. It will continue to rise, at an increasing rate, until the diaper is changed or the urea exhausted.
Ammonia is small, polymorphous, and highly soluble in water, and is highly mobile. Ammonia is also soluble in lipids and can migrate across many cell membranes. As the skin pH increases through the 7.0 to 9.0 range, the alkalinity overcomes the lactic acid buffering capacity of the epidermis and inflicts caustic burning, causing ammonia dermatitis. In addition, ammonia gas is also a suffocant that can cause life-threatening stenosis or, if inspired suddenly, gastrointestinal reflex/reflux. Furthermore, ammonia is a sedative that, if inspired gradually over time, can impair an infant""s central nervous system and medullary and adrenocortical functions.
A major concern regarding long-lasting, leak-proof diapers is that the urine permeable membrane enclosing the absorbent matrix often leaks or ruptures, most often during the time period after urine pH has reached about 8.5. During this period, free ammonia continuously builds up within the diaper, and fluid pressures will continue to build within the absorbent core. The pressures of the fluids and gases against the diaper""s liquid permeable topsheet matrix membrane are said to have reached the breakthrough point when an external mechanical pressure of 0.5 psi forces fluids and gases to reverse-permeate the diaper""s liquid permeable topsheet and contact skin. Such mechanical pressures can include the wearer rolling over or the diaper being forcefully pressured by unyielding objects, such as crib siding, a car seat or a wheelchair. When the pressures within the sheath increase past the breakthrough point, the topsheet may leak or rupture, releasing toxic dissolved and free ammonia and carbon dioxide. The matter released may contain a significant biomass inoculum of rapidly multiplying bacteria including Proteus supp. This highly toxic mix contacts skin, and, if present, feces and pre-existing lesions.
U.S. Pat. No. 4,231,370 to C. Mroz et al. relates to a disposable diaper having a wetness indicator that is a pH-change/color-change stripe visible from the exterior of the diaper. The indicator comprises an absorbent color-change material (bromophenol blue) in a matrix of highly flexible latex adhesive. This indicator only indicates wetness; it does not measure or indicate pH changes or ammonia concentrations.
U.K. Patent No. 2 250 121 to Lee relates to a disposable diaper wherein moisture closes a circuit, activating an audible alarm signaling that the diaper is wet.
French Patent No. 2 680 678 to Ly relates to the use of a moisture sensor linked to a transmitter in a diaper that sends a signal to a receiver kept by parents.
The prior art that notifies caregivers of wetness in a diaper has some utility since wet skin is more vulnerable to damage than dry skin, but short-term wetness, in itself, is not damaging. Diaper-area wetness becomes dangerous to healthy skin only in conjunction with other irritants. Prior art wetness indicators that rely on pH measurement function in a binary mode; that is, they indicate simply whether an article is wet or dry, with no indication of the degree of wetness. A pH indication based solely on the presence of urine is useful, but does not indicate whether the urine is decomposing and therefore shifting to a more alkaline pH, which will lead to an unsafe environment. While the prior art attempts to solve the urine-ammonia problem at its source, until now there has been no method for warning the caregiver that the harmful conditions are imminent.
The present invention provides a method and apparatus for warning the caregiver of a diaper-wearer when the pH concentration within the diaper approaches a degree of toxicity that can cause or exacerbate damage to the wearer""s skin and other membranes.
With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several views illustrated in the drawings.